1. Field of the Invention
The present invention relates to an image forming method making use of a recording medium comprising a recording layer containing a polymeric liquid crystal compound, and more particularly to an image forming method that utilizes changes in alignment. It also relates to a recording medium that can be used in such an image forming method. It still also relates to a method of reproducing an image formed by such an image forming method.
2. Related Background Art
In a conventional digital electrophotographic system, information signals are recorded on a photosensitive member by operating "on-off" according to information signals while a semiconductor laser beam is scanned on the photosensitive member utilizing a polygonal mirror. In such a system, however, it is necessary to increase the output from a laser or deliver the output for a long time when a highly detailed image is recorded or an image is recorded at a high speed, in particular, when the same image is recorded on a large number of sheets. Hence, a problem has tended to arise on the durability of the laser itself. When images are continuously read in and recorded, the same image is repeatedly read in, and hence, a large load is applied to an optical scanner.
Moreover, it is difficult for semiconductor lasers to serve as laser light sources for R, G and B corresponding with a color image, making it necessary to provide a large-scale and complicated apparatus.
An analog recording system, on the other hand, is exemplified by a system called a screen process in electrophotography, according to which an intermediate image is obtained on an intermediate transfer medium in the form of ion recording. This system, however, has an instability ascribable to ion charging, and it has been impossible to obtain a long-term memory performance.
A diazo recording system, having been in great demand because of a low running cost, has also been disadvantageous in that no copy can be taken from a three-dimensional object and also disadvantageous in that it can not handle color images.
As for image forming materials that are reversibly image-erasable and repeatedly usable, having a possibility of being utilized as intermediate image holders, what can be considered useful are photochromic materials, thermochromic materials, magnetic recording materials, or liquid crystals sandwiched between glass plates.
However, use of a photochromic material as the intermediate image holder requires irradiation on a photochromic layer in order to optically record an image on a photosensitive layer, since light is used as a means of recording or erasing the image on or from the photochromic material. This tends to cause changes in the photochromic layer or brings about a problem in its durability.
Thermally reversible Ag.sub.2 HgI.sub.4 has been reported as a thermochromic material. The material of this type, however, has no storage capability, and hence a heater must be always operated so that an image can be retained. There results not only in a large-scale and complicated apparatus but also in a large power consumption.
As a further example, an intermediate image holder making use of a liquid crystal light valve is usually comprised of a low-molecular smectic liquid crystal held between glass substrates, where a laser light absorbing layer is provided in the cell and its homeotropic alignment is brought into a scattered state by heating with external irradiation using a laser, thereby to obtain a contrast. This image holder, however, can not be made to have a large area with ease on account of its structure, or has a complicated structure for an intermediate image holder because erasure is effected by electric-field alignment. It is also difficult to directly write an image using a heating-element head on account of the structure of the device. Taking account of the fact that the image holder can not be made to have a large area, it is attempted to carry out the irradiation using a high-luminescence light source to project an enlarged image. There, however, is the disadvantage such that the irradiation deteriorates the intermediate image because of a poop heat stability.
To cope with such problems, polymeric liquid crystal compounds have been proposed as materials capable of showing superior performances.
Recording mediums making use of polymeric liquid crystal compounds can be exemplified by a thermal write memory disclosed in V. Shibaev, S. Kostromin, N. Plate, S. Ivanov, V. Vestrov and I. Yakovlev, "Thermotropic Liquid Crystalline Polymers. 14", Polymer Communications, Vol. 24, pp. 364-365.
However, because of a delay in response speed that concurrently occurs as increase of molecular weight of the material, these have not been put into practical use. To overcome such disadvantages, it has been proposed to achieve a higher speed by the use of a photoconductive layer (Japanese Patent Application Laid-open No. 64-7022).
The above prior art, however, in which the device is so constituted that a recording layer and the photoconductive layer are held between a pair 0f electrode substrates, can not be satisfactory for the use of light as a means for writing, in resolution and contrast.